This might help: http://pitchdeckcoach.com/pitch-deck.
Think of your tagline as the tip of your pyramid. Your elevator pitch is the next level down. And you pitch deck is the base of the pyramid. Your elevator pitch should be a 30 second summary of your pitch deck and your tagline should be a 10 second summary of your elevator pitch.
In the example I link to above the tagline would be something like: "On demand mobile auto detail for busy office workers"
For investors, you can sometimes use a comparative tagline.
Investor version: Lending Tree for real estate agents
Consumer version: Let real estate agents compete to sell your home.